Interesting experiment with ADSL splitter

Discussion in 'Computing and Networks' started by Jeniffer Chris, Nov 26, 2013.

  1. Jeniffer Chris

    Thread Starter New Member

    Nov 24, 2013
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    As we know, the ADSL splitter box has 1 input and 2 outputs, one for phone signal line, and the other for internet signal line
    Plug the telecommunication line into the input. Then in the output lines, I make the exchange. I plug the phone line to the internet output, and the internet line to the phone output
    Then I dial the phone to call to a fax number
    Surprisingly, I heard the busy tone, instead of fax tone.
    Note: When I connect in normal way, plug the phone line to the phone output, and internet line to the internet output, this effect does not happen. That means I heard the fax tone as usual

    Second experiment

    I have been considering what happens if I make the feedback from out put to input of a ADSL splitter, as well as change input to output and vice versa
    Below are my steps:
    - Take the first splitter, plug the phone line to the Net output (NOT the input) of it
    - Plug the input of the first splitter to the input of the second splitter
    - Plug the Phone output of the second splitter to the phone output of the first one
    - Plug the Net output of the second splitter to Modem, and connect to laptop

    See diagram in my attached screenshot

    Here I made some abnormal things:
    - Telephone signal transmits into the output, not the input of the splitter
    The output of second splitter is connected back to the first one

    Surprisingly, my laptop can access internet normally. Nothing wrong happens
    Why my extraordinary actions do not affect the operation of the splitters?
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    My ADSL filters all just have two ports: Line in and Phone out. They are just a low-pass filter which prevents the phone from loading the line at DSL frequencies. The DSL modem connects to the incoming line without a filter in front of it; everything else gets a filter.

    I cheated. I put just a single filter into the entrance box. The entire house/hangar is wired with RJ-11s. The Red-Green pair is the filtered line for phones and fax, the Yellow-Black pair is the unfiltered pair. Now I can plug a phone anywhere in the house/hangar (Red-Grn pair) without screwing with a DSL filter. The only place the Yel-BlK pair gets connected is into the DSL modem. However, I can move the modem to any RJ11 without messing with filters...
     
    Last edited: Nov 26, 2013
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    MY ADSL uses one line. I just put filters for the phones.
     
  4. rst1

    New Member

    Nov 26, 2013
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    1
    Hi Jeniffer,
    I'm not positive what device you are using. The one I am familiar with is this one http://www.wilcominc.com/Assets/product_full/PS-36.jpg . assuming that the two are similliar, there is a low pass filter between the input and phone connections. There is a bit of wire between the input and net ports. The labels that differentiate these two ports are for human convenience. This means your second scenario is exactly expected behaviour. (although there will be a minuscule signal degradation due to increased resistance) You didn't say, but I suspect that the internet didn't work in your first scenario. The fax ringing busy is strange, unless you happened to call just when the fax was busy. (i.e. the fax was already on the line.) I would be interested if this is reproducible.
    Ray
     
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  5. WBahn

    Moderator

    Mar 31, 2012
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    I've had similar experiences when calling a fax line. I've always just assumed that the fax was in use.

    Have you tried repeating the experiment?
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    I cheated in a somewhat different way. It turned out that the jack I wanted the modem at happened to be on the wall near where the demarc was. So I took a guess that it was the jack that was wired first and that the rest went from there. So I disconnected the wires on the jack and, sure enough, none of the phones in the rest of the house worked. So installed the filter in the utility box and wired it to send the filtered signal on to the rest of the house while bring the unfiltered signal to that particular jack. The modem itself had a filtered phone output, so that worked great for the phone I wanted in that room. If I had ever moved the modem to a different room, I would have rewired box to do what you did, but I never ended up wanting to move it.
     
  7. Jeniffer Chris

    Thread Starter New Member

    Nov 24, 2013
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    Yes, that's why I named my topics 'interesting experiment'.

    I replicate this scenario many times, and got the same result.

    Whenever I connect in the right way, phone line plugged to phone jack, net line to net jack, I can hear the fax tone. But when I swapped between them, busy tone is heard
     
  8. Jeniffer Chris

    Thread Starter New Member

    Nov 24, 2013
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    There is a suggestion for me that, to make a REAL looping from output to input, I must cut inside the cable, and splice the red to the green and other green to the other red

    It's unlucky that this action is very difficult to do in actual, since it requires very skillful person
     
  9. Jeniffer Chris

    Thread Starter New Member

    Nov 24, 2013
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    I tried to cut inside the cable, and connect the wire, each by its color

    In a), I loop the net output to input, and connect phone output to a telephone machine. No signal at all

    In b), I loop the phone output to input, and connect net output to a modem, this time I can access internet normally

    Is it working correctly?
     
  10. Ramussons

    Active Member

    May 3, 2013
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    Are you sure you are getting a "busy" tone and not a "timeout" tone?
    Have you tried dialling a non fax number? What happens?

    Ramesh
     
  11. Jeniffer Chris

    Thread Starter New Member

    Nov 24, 2013
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    Sure, it is really busy tone

    For a phone and non-fax number, it works well
     
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